vessel provided with a device for removing and/or installing a sub-structure of a driling or production platform

ABSTRACT

The invention relates to a vessel ( 1 ) provided with a deck ( 2 ) and with a device ( 3 ) for removing and/or installing a sub-structure ( 4 ) of a drilling or production platform, wherein said device comprises a supporting structure ( 5 ) which is capable of tilting movement in a direction transversely to an edge ( 6 ) of the deck ( 2 ), hoisting means ( 7 ) connected to said supporting structure for hoisting said sub-structure, and supporting means for supporting said sub-structure mainly during tilting movement of said supporting structure, wherein said supporting means are provided separately from the supporting structure and capable of tilting movement with respect to the edge of the deck.

[0001] The invention relates to a vessel provided with a deck and with adevice for removing and/or installing a sub-structure of a drilling orproduction platform, wherein said device comprises a supportingstructure which is capable of tilting movement in a directiontransversely to an edge of the deck, hoisting means connected to saidsupporting structure for hoisting said sub-structure, and supportingmeans for supporting said sub-structure mainly during tilting movementof said supporting structure.

[0002] Such a vessel is disclosed in prior Dutch patent application no.1012314 (not prepublished). The supporting structure of said vesselcomprise two support beams. Each support beam is provided withsupporting elements on its side remote from the vessel, which supportingelements function to support the sub-structure during tilting movementthereof. Furthermore, each support beam is fitted with hoisting means atits upper end remote from the deck. In order to provide adequate supportfor a sub-structure, which generally comprises downwardly diverginglegs, during tilting movement thereof, said supporting elements aremovable transversely to each support beam.

[0003] The object of the present invention is to provide a vesselcomprising a device for removing and/or installing a sub-structure,wherein said removing/installing device has been improved.

[0004] According to the invention, the supporting means are providedseparately from the supporting structure and are capable of tiltingmovement with respect to the edge of the deck. The points of support canbe set independently of the hoisting points and be adapted to thesub-structure that is to be removed, as a result of which a moreflexible removing/installing device is obtained.

[0005] Preferably, said supporting means comprise a beam. Said beam onlyhas a supporting function, it is no longer needed in order to provide ahoisting point, so that said supporting beam can have relatively smalldimensions. As a result, the bending moments exerted during tilting willbe small, which makes it possible to use a light-weight and narrow beam,which enables a saving in material and thus in weight.

[0006] In a very advantageous embodiment, said supporting means comprisetwo beams, at least one of which is movable along the edge of the deck.This makes it possible to adapt the supporting means to thesub-structure that is to be removed: the beams are spaced closertogether or further apart in dependence on the position of the legs ofthe sub-structure that are to be supported.

[0007] In one advantageous embodiment, said supporting structurecomprises a portal, wherein the hoisting means engage the cross beam ofthe portal.

[0008] If the hoisting means are movable along said cross beam, aflexible removing/installing device is obtained, by means of whichsub-structures of varying dimensions, for example sub-structures havingfour, six, eight or ten legs, can be removed.

[0009] In a very advantageous embodiment, said supporting structureconsists of two portals which are connected to the edge of the deck,having a common tilting axis, and whose legs include an angle betweenthemselves. Each portal functions to support and hoist one side of thesub-structure, towards the vessel and away from the vessel,respectively.

[0010] Preferably, the angle between the cross beams of the portals isadjustable, so that it is possible to adjust the distance between thehoisting means and the sub-structure to be removed. In the case ofrelatively large sub-structures, the angle between the portals can beenlarged, so that the hoisting means will be spaced further apart; inthe case of relatively small sub-structures, a smaller angle between theportals will be used so as to move the hoisting means closer together.

[0011] The device for removing and/or installing a sub-structurefurthermore comprises tilting means for tilting the supporting structurerelative to the vessel. According to an advantageous embodiment of theinvention, said tilting means comprise a winch mounted on the deck andone or more winch cables provided between said winch and said supportingstructure. In addition to this, said tilting means preferably comprise astay fitted between the deck and the supporting structure, wherein thepoint of engagement between said supporting structure and said stay ismovable. It is known to use such a structure for telescoping the legs ofa drilling platform, in order to make it possible to install saiddrilling platform on the seabed after towing. The advantage of such aconstruction is that it is possible to take up a relatively large forcewhile using a relatively light structure.

[0012] The invention will now be explained in more detail with referenceto the appended drawings, wherein:

[0013]FIG. 1 is a perspective view of a vessel provided with a devicefor removing and/or installing a sub-structure in accordance with onepreferred embodiment of the invention;

[0014]FIG. 2 shows the vessel of FIG. 1 with the removing/installingdevice in different working position; and

[0015]FIG. 3 is a perspective detail view of the removing/installingdevice of FIG. 1.

[0016]FIG. 1 is a perspective view of a vessel 1 provided with a deck 2and a device 3 for removing and/or installing a sub-structure 4 of adrilling or production platform. Said removing/installing device 3 ispositioned mainly on the starboard side of the vessel, and it comprisesa supporting structure 5, which is capable of tilting movement in adirection transversely to the edge 6 of deck 2 on the starboard side ofvessel 1. Removing/installing device 3 furthermore comprises hoistingmeans 7 for hoisting the sub-structure 4, wherein said hoisting means 7are connected to supporting structure 5. Supporting means in the form oftwo beams 8, which are tiltable relative to edge 6 of deck 2, areprovided separately from the supporting structure 5 for the purpose ofsupporting sub-structure 4 mainly during tilting movement of supportingstructure 5. At least one of the beams 8 can be moved along the edge 6of the deck 2 so as to adapt the spacing between beams 8 to thedimensions of the sub-structure 4 that is to be removed. According toanother possibility, both beams 8 are movably disposed near the edge 6of deck 2.

[0017] Supporting structure 5 comprises two portals 9 a, 9 b, eachhaving two legs 10 a, 10 b and one cross beam 11 a, 11 b. Hoistingcables 18 are suspended from each cross beam 11 a, 11 b. Said hoistingcables 18 can be taken in and paid out by means of pulleys and wincheson deck 2 or by means of cable jacks. The specific type of hoistingmeans is of little relevance for the invention, and consequently it willnot be further described herein. To those skilled in the art it is clearwhat variants are possible. It should be noted, however, that thehoisting means 7 are preferably movable along cross beams 11 a, 11 b.Because distances of about 30-40 m need to be bridged, a pull/pushcylinder 12, for example, or a rack-and-pinion drive may be used forthis purpose.

[0018] The two portals 9 a, 9 b have a common tilting axis 13 near theedge 6 of deck 2. In addition to this, portals 9 a, 9 b are connected tothe vessel in such a manner that their legs 10 a, 10 b include an anglebetween themselves. The angle between cross beams 11 a, 11 b of portals9 a, 9 b can be adjusted by means of cables 14 provided between saidcross beams and reels (not shown) for winding and unwinding cables 14.Said mechanism can preferably be operated by remote control.

[0019] Removing/installing device 3 is furthermore provided with tiltingmeans for tilting portals 9 a, 9 b relative to vessel 1. Said tiltingmeans consist of two winches 15 mounted on deck 2, with winch cables 16provided between winches 15 and supporting structure 5, and two stays 17fitted between deck 2 and supporting structure 5. In the preferredembodiment as shown in the drawings, winch cables 16 are fixed to therear portal 9 b, that is, the portal positioned nearest deck 2, andstays 17 engage the front portal 9 a, that is, the portal positionedfurthest away from deck 2. The point of engagement 19 between frontportal 9 a and each stay 17 is movable (compare FIGS. 1 and 2).

[0020] Since the portals 9 a, 9 b of supporting structure 5 have acommon tilting axis 13, the cross beams 11 a, 11 b describe a segment ofa circle during tilting. The spacing between cross. beams 11 a, 11 b ofportals 9 a, 9 b, and thus the spacing between the hoisting means 7 thatare present at that location, remains constant thereby.

[0021] The removal of a sub-structure 4 by means of the vessel 1according to the present invention will now be explained with referenceto FIGS. 1 and 2. Starting from the working position of theremoving/installing device 3 as shown in FIG. 1, the hoisting cables 18are fixed to the upper ends of the legs of sub-structure for example bymeans of hydraulic clamps or crane hooks. Sub-structure 4 is lifted byhoisting means 7 in such a manner that sub-structure 4 comes intocontact with beams 8. Then the supporting structure 5 is tilted abouttilting axis 13 by operating the winches 15. The winch cables 16 pull atthe rear portal 9 b, which pulls the front portal 9 a along via cables14. During tilting, the center of gravity of sub-structure 4 will at alltimes be located on the side of tilting axis 13 remote from vessel 1.Upon reaching the dead center, the supporting structure 5 is preventedfrom tilting further by the stays 17 that support the two portals 9 a, 9b (see the working position of the removing/installing device 3 in FIG.2). The supporting beams 8 support the sub-structure 4, or rather, guidethe tilting movement of sub-structure 4 immovably during tilting. Therelatively small dimensions of beams 8, and thus the low bendingmoments, enable a relatively light-weight construction of the beams. Thetwo supporting beams 8, or at least parts thereof, are movably mountedalong edge 6 of deck 2 so as to enable adjustment of the spacing betweenbeams 8 of the sub-structure 4 that is to be removed. Sub-structure 4 issupported near its legs during tilting, since these parts of the latticestructure of sub-structure are sufficiently strong for this purpose. Inthe case of a sub-structure having four legs, the outer legs will besupported, in the case of a sub-structure 4 having 8 legs (as shown inthe figures), the two inner legs will be supported. In order to enablemovement of beams 8, portals 9 a, 9 b may be fitted with auxiliaryhoisting means 20, which can be moved along cross beams 11 a, 11 b witha load being exerted thereon. Furthermore this makes it possible to usethe supporting structure 5 with auxiliary hoisting means 20 as a cranefor placing constructional components of a drilling or productionplatform, for example, onto deck 2 or removing them therefrom. Beams 8remain present on deck 2 thereby, and only portals 9 a, 9 b are tiltedin order to move the constructional component to be removed from outsidevessel 1 between the legs 10 a, 11 b of portals 9 a, 9 b and place itonto deck 2, or vice versa. Since the constructional component that isto be removed does not tilt along with the portals, it is necessary inthat case to adjust the angle between portals 9 a, 9 b during tilting,in such a manner that the spacing in horizontal direction between theauxiliary hoisting means 20 on the two cross beams 11 a, 11 b remainsthe same.

[0022] Finally it is noted that the sub-structure 4 can be moved furtheronto the deck 2 after tilting, for example by means of the winches.

[0023] Although the invention has been explained by means of adescription of the removal of a sub-structure, the vessel can also beused for installing a sub-structure, of course.

1. Vessel provided with a deck and with a device for removing and/orinstalling a sub-structure of a drilling or production platform, whereinsaid device comprises a supporting structure which is capable of tiltingmovement in a direction transversely to an edge of the deck, hoistingmeans connected to said supporting structure for hoisting saidsub-structure, and supporting means for supporting said sub-structuremainly during tilting movement of said supporting structure,characterized in that said supporting means are provided separately fromthe supporting structure and are capable of tilting movement withrespect to the edge of the deck.
 2. Vessel according to claim 1,characterized in that said supporting means comprise a beam.
 3. Vesselaccording to claim 1 or 2, characterized in that said supporting meanscomprise two beams, at least one of which is movable along the edge ofthe deck.
 4. Vessel according to any one of the claims 1-3,characterized in that said supporting structure comprises a portal,wherein the hoisting means engage the cross beam of the portal. 5.Vessel according to claim 4, characterized in that said hoisting meansare movable along said cross beam.
 6. Vessel according to any one of theclaims 1-5, characterized in that said supporting structure consists oftwo portals which are connected to the edge of the deck, having a commontilting axis, and whose legs include an angle between themselves.